1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to an integral compressor and centrifugal fuel pump.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A small gas turbine engine operates at a very high rotational speed because of its size. A fuel is mixed in the combustor with pressurized air and burned to produce a hot gas flow which is then passed through the turbine to drive the compressor and a bypass fan if used. Some prior art engines use a plurality of individual fuel injectors spaced around the combustor and inject fuel directly into the combustor. Enough injectors are required so that a fairly even combustion pattern is created within the combustor. Using many injectors will also increase the cost and complexity of the engine.
Some prior art small gas turbine engines use a slinger to compress and sling the fuel into the combustor in a radial outward direction. A slinger delivers the fuel into the combustor around a full 360 degree pattern (referred to as a zero pattern factor) so that a uniform distribution of fuel in the circumferential direction is formed. However, the slingers do not pressurize the fuel to a high pressure. High fuel pressure would help to atomize the fuel to a fine mist which would help to improve combustion efficiency.
Another problem found in a small gas turbine engine is the difficulty of providing a fuel pump that can supply adequate fuel pressure at the very low fuel flow rates inherent in a small thrust turbine engine.
U.S. Pat. No. 6,983,606 B2 issued to Brown on Jan. 10, 2006 and entitled INTEGRATED GAS TURBINE COMPRESSOR-ROTARY FUEL INJECTOR discloses a small gas turbine engine with a centrifugal compressor having a contoured rear surface extending inboard and terminating at a lip to form a surface on which a fuel is forced along the surface and into the combustor in an axial direction. Rotation of the centrifugal compressor forces the fuel along the surface and into the combustor. Since the surface over which the fuel passes is uncovered, the pressure of the fuel is not increased very much.
Another problem with small gas turbine engines is in atomization of the fuel. The fuel must be broken up into very fine particles of fuel in order to burn fast in the combustor. Large particles will take longer to burn and therefore require a longer combustor in order to allow for enough time for the large fuel particles to burn completely before passing into the turbine section. However, forming small droplets of fuel require higher pressures than would be produced in the prior art engines. Larger engines can make use of separate high pressure fuel pumps to provide the higher pressures required for adequate atomization of the fuel. However, adding additional parts such as separate fuel pumps add weight and size, as well as complexity, to small a gas turbine engine. In the case of a cruise missile, eliminating unnecessary space and weight would allow for more fuel to be carried, resulting in longer range or increased loiter time.
U.S. Pat. No. 2,568,921 issued to Kroon on Sep. 25, 1951 and entitled COMBUSTION CHAMBER WITH ROTATING FUEL NOZZLES discloses a gas turbine engine with a rotary ducted impeller element carried on the rotary shaft that has four fuel nozzles at the duct end to inject fuel into the combustor in the axial direction of flow. The rotary ducted injector is capable of rotating at 12,000 rpm to produce a fuel pressure at the nozzles in excess of 3,000 psi to sufficiently atomize the fuel. Fuel is pumped under low pressure into a collecting chamber at the inlet of the radial ducts. One problem with the rotary ducted injector of the Kroon invention is that the injectors and radial ducts are located within the hot combustor, exposing the fuel injector assembly to the extreme high temperature environment of the combustor. This would most likely lead to coking of the hydrocarbon fuel within the fuel passages and subsequent restriction or plugging of the fuel flow. Another problem with the Kroon invention is the use of a radial ducted fuel injector which can be affected by rotor imbalance forces leading to further imbalance. This is because the rotor of any machine is not perfectly balanced. The geometric center of the rotating member will not be the center of rotation due to mass imbalance inherent in any imperfect part. Without a compensating fuel feed system, the Kroon invention would likely cause significant rotor dynamics problems and would not work in a real engine.
An object of the present invention is to provide for a high pressure fuel injector in a small gas turbine engine without requiring a massive and heavy fuel pumping system.
Another object of the present invention is to modify a centrifugal compressor of a gas turbine engine such that the compressor can also be used to pressurize and deliver the fuel to the combustor.
Another objective of the present invention is to provide for improved balance to a rotating injector of the prior art.